This application claims priority of European Patent Application No. 98307490.7, which was filed on Sep. 15, 1998.
The present invention relates generally to the field of cellular radio networks and a method for operating cellular radio networks, particularly a method for providing adaptive neighbor cell lists for a cellular radio network.
The basic idea underlying cellular radio networks is to use within a limited band width only a given number of frequencies for setting up radio channels. The given frequencies are used several times to provide the traffic capacity required despite the limited bandwidth. For this purpose every cell of the cellular radio network uses only one frequency or a subset of frequencies from within the available bandwidth. Neighboring cells do have different frequencies or subsets of frequencies. Cells using the same frequency or subset of frequencies are located sufficiently far from each other. In that way signal strengths of the different radio channels represented by the different frequencies have decreased sufficiently in order to avoid disturbances caused from co-channel interference.
In order to achieve seamless coverage and to support the traffic capacity required, a number of system parameters for the design of the cellular radio network has to be considered, e. g. traffic intensity in different areas, maximum transmission power and interference. When the design of a cellular radio network is completed, a dedicated group of frequencies is allocated to each cell, i. e. a number of carriers having the given frequencies.
Ongoing calls are handled by the cellular radio networks by using handovers. If a mobile station (MS) having an ongoing call leaves one cell or if the reception conditions for that cell, i. e. the reception conditions for the frequency used, deteriorate the MS is handed over to that neighboring cell which offers the best reception. To achieve this, handover algorithms are used in the cellular radio network. Usually the MS monitors the reception quality of the serving cell and a number of neighboring cells and sends the information on the reception quality to a base station transceiver (BTS) of the serving cell. The information is then transmitted to a base station controller (BSC). BTS or BSC decides on necessary handovers. The BSC provides a list to the MS, containing the neighbor cells of the serving cell which have to be monitored by the MS. In common cellular radio networks the size of the neighboring cell list is limited, e. g. to information on 32 neighboring cells. This limitation causes a restrictions to the operability of the cellular radio network, if the cellular radio network has a complex cell structure employing e. g. macro cells with an underlying structure of micro cells. For complex cell structures like the mentioned one, the limitation to 32 neighboring cells in the neighboring cell list may cause problems to identify the cell offering the best reception, because not all neighbouring cells can be monitored.
Accordingly, it is an object of the present invention to provide a method for providing neighbor cell lists for a cellular radio network. It is the aim of the inventive method under consideration to avoid the drawbacks known from the state of the art.
The object is achieved by providing a method for operating a cellular radio network having neighbor cell lists comprising steps of providing a first part of the neighbor cell list containing information on fixed neighbor cells, and providing a second part of the neighbor cell list containing information on varying neighbor cells.
It is an advantage of the present invention, that it allows to adapt the neighbor cell lists according to the actual location of a mobile station and the actual reception conditions at the time the mobile station is operative.
The present invention will become more fully understood from the detailed description given hereinafter and further scope of applicability of the present invention will become apparent. However, it should be understood that the detailed description is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.